In January, 1971, a collaborative project was undertaken by six centers, the Univ. of Colorado, the Univ. of Oregon, the State Univ. of N.Y. at Buffalo, Harvard Univ., the Univ. of Pennsylvania and the Univ. of Tenn., to perform chromosomal analyses on 11,000 7 and 8 year old children enrolled in the NINDS collaborative study on cerebral palsy and mental retardation. This study was designed in essence as a prospective study to establish clinical-karyotype correlations in the subjects, since they constitute a random sample (with the exception of mortality within the first 7 years of life). Originally, technics in the 6 participating labs were standardized, using long established staining procedures. After the first year, technics were changed to include newly acquired procedures for specific chromosome identification. This involved a significant additional workload on lab personnel, and was done without additional funds. The present request is submitted to allow completion of the project, put behind schedule because of the extra workload, to allow resampling of failed cultures, and to allow more complete sampling by recontact of subjects not originally sampled. In addition, the additional time will allow followup and further investigation of subjects in whom abnormalities have been found, and their families. Information regarding analysis of data is submitted in the request from the Univ. of Colorado Center.